Brother's End
by Bradykins98
Summary: When a young Ultramarine sergeant is mysteriously spared by a Night Lords champion unlike the rest of his squad, he goes on a near suicidal solo mission to hunt the Chaos Marine down. Along the way, he is forced to make choices that affect his view of humanity, the Codex Astartes, and even the Imperium itself. T for violence.
1. Chapter 1

Brother's End

A Warhammer 40,000 story

Prologue

One month earlier, the Cleansing of Pinscillus IV …

"Marcellus, Castor, hit the heretic's right flank!" He ordered through his vox-system. Two green flashes on his helmet's HUD confirmed the said marine's acknowledgement. He hacked at a cultist with his chainsword, spraying blood over his golden Imperial Eagle. From his right, he heard the steady chatter of bolter fire, cutting down several cultists with the self-propelled rounds turning the screeching heretics into chunks of gore and bone.

"Need a hand, Brother-Sergeant?" A blue-armoured silhouette spoke up, stalking across the battlefield to him. Andros probably had that cocksure smile that he always had plastered on his face, whenever he was in battle. He still believed that he was invincible, a belief that being a Scout hadn't knocked out of him yet. He nodded towards the younger tactical marine, a silent thanks for dealing with the cultists.

"Brother Andros, with me. Time to hunt down the ringleaders of this cult." He ordered.

"Well said Brother-Sergeant. Time to win some glory for Macragge eh?" The younger marine answered.

"Glory is not what we fight for. We fight for the Emperor, and the good of the Imperium. Glory is for the Assault Marines, anyway." He joked half-heartedly. Andros gave a harsh bark of laughter, a trait of his home-world of Calth.

They heard gunfire up ahead, the low drum-beat of a heavy bolter combined with the sharp crack of lasguns. The two Ultramarines ran forward, bolters in hand, towards the sounds of battle. Up on a high ridge overlooking the battlefield, Castor and Marcellus had positioned themselves to a suppressing position on the cultists below, the heavy bolter carried by Marcellus providing a great weight of fire. Castor had yet to ready his plasma gun, which had overheated, slightly scorching the tactical marine's forearm armour. Andros fired his bolter on single-shot as he walked forward, to gain greater accuracy as he moved forwards. He strode across the middle of the battlefield, seemingly unaware of the las-blasts that were bouncing off his power armour.

The enemy started dropping mortar shells on the Astartes's position. Shrapnel peppered his power armour, bouncing off and merely scratching the paint. He raised his bolter and fired a burst off with one hand, whilst running to cover. He could see Andros still advancing, oblivious to the amount of fire he was taking. His armour wouldn't be able to take much more punishment. "Andros, find cover now!" He barked through the vox bead in his helmet.

"But Brother-Sergeant, I can clear their first line of defence." Andros' reply almost sounded like a small child moaning to their father. Castor's plasma gun had cooled down, and he was laying well-placed shots on enemy heavy stubber posts and mortar nests with impunity.

"Andros, you'll get yourself killed. Get into cover now." He roared at the defiant marine. As he expected, Andros' armour couldn't hold up to any more bombardment.

A single shot cracked out across the battlefield as Andros' helmet cracked then burst open, spraying his brains across the half-dead grass. His lifeless (and headless) corpse staggered a couple of paces then fell into the dirt. The shot came from a bolter, he was sure of that; and at a range of three hundred yards; the firer was clearly a trained shot. He poked his head out of the crater he had dived into. He saw a faint scope glint on top of a wrecked Leman Russ tank.

He magnified the image using his helmet's optical systems, and sure enough there was a sniper. He couldn't get a clear look at the sniper though, as he was mostly covered by the tank's turret, but from what he could see, the sniper was wearing thick dark blue armour.

"Castor, you see the wrecked Leman Russ three hundred yards to my east?" He asked over the vox channel.

"Yes, taking it out now." Castor correctly guessed his intention with the question. He saw a flash of superheated plasma flash past his right, and explode in a ball of blue flame. Sure enough, a body fell from the explosion. But despite the armour the body was wearing bubbling and dripping off, he could still see the familiar outline of power armour.

"Watch for Chaos Marines in their ranks, the sniper Castor took out was one of these treacherous scumbags." He warned the rest of his squad. Eight icons flashed green to confirm they understood. Eight, when there should have been nine.

Then he heard an almighty roar coming from the Chaos lines. Suddenly a whole wave of cultists surged forward, coming out of foxholes and trenches by the dozen. Marcellus's heavy bolter cut them down in droves, the mass reactive rounds quite literally tearing them apart. Castor's plasma gun fired bolt after bolt, overheating in under a minute.

He heard bolter fire coming from behind him, and saw on his mini-map that the rest of his squad were firing as well. He unclipped a frag grenade, and lobbed it at least twice as far as any human could ever manage. It exploded, sending shrapnel everywhere, shredding the charging cultists.

He fired a magazine from his bolter before drawing his chainsword. He slung his bolter and thumbed the activation rune on the hilt of his sword. The blade roared to life with a growl, and he burst from cover, charging straight into the screaming mass. He shoulder barged the first cultist, smashing its face on his stylised U. He swung his chainsword, the whirring blade cutting three cultists in half. With his free hand he lashed out, catching another cultist in the face and sending the flailing man flying into two more of its kin. He parried the clumsy downward swing of a rusty steel blade and decapitated the owner. Ducking a las-pistol to the face, he kicked out at the assailant, crushing the cultist's ribcage.

Despite his bulky appearance, he was very agile and light on his feet. It was a fatal misconception for many.

Suddenly Althrax's rune flashed red on his visor. He frowned, what could have taken him down? Then Michelus's, then Balthas's, then Pollux's. Half his squad had been killed.

"Brother-Sergeant, traitor-marines to your-" Marcellus's transmission was cut out by a deafening series of explosions that rocked the battlefield. The cliff that Castor and Marcellus were firing from collapsed, impacts from large shells pummelling the rock to pieces. Both marine's runes flashed red. From the dust cloud in the Chaos lines strode a massive figure, easily the same size as he was.

The figure was wearing power armour, but it was an old version, that was covered with sigils and runes that burned bright orange. The armour was a dark, almost black, blue, and there were much gold trimmings on it. The figure wasn't wearing a helmet, which revealed bloodshot eyes, bleached white skin and teeth that clearly hadn't been seen by a toothbrush in decades. The figure, clearly a Chaos Space Marine of some importance, held a massive auto-cannon, which he promptly dumped unceremoniously, unsheathing a glowing obsidian blade. He was the one who had caused the deaths of his squad.

Behind him, at least a dozen more Chaos Marines stepped forward. He recognised the insignia on their shoulder pad's to be that of the Night Lords. He ordered the remaining two members of his squad to rally on him. After a few moments of brutal combat, Natoris was at his back; a few moments after that so was Cato.

"I don't want to lie to you. It's likely that this is our last battle. But I for one will not bow down to these traitorous bastards and be killed like a whimpering dog. I'll sell my life dearly, with my ammo spent, my sword broken, my hands round an enemy's throat. You will to, for you are Ultramarines! You are warriors of the Emperor, the Adeptus Astartes, and apart from being in a drop pod, you know no fear!" He roared, trying to encourage the last of his squad. They knew as well as he did that this would be their last. He reloaded his bolter, and held it in his right fist. If he was going to die, then so would many of them.

He roared a wordless battle-cry and charged head-first into the Chaos horde. His two squad-mates were at his flanks, both with wordless cries on their lips as well.

They burst forward, to be met by the mass of the cultists. However, an angry Space Marine is akin to an erupting volcano, dangerous, gigantic and uncontrollable. They hacked and slashed and shot and stomped and kicked and punched their way through the cultists. His armour took dozens of wounds without the machine-spirit's complaint.

He fired an entire magazine on full-auto one handed, turning at least fifteen Chaos worshipers into something akin to mashed watermelons. He could see out of the corner of his visor that his two fellow marines were fairing just as well as he was. Within minutes of butchery, the few cultists that remained were fleeing.

As the ordinary men turned around and ran, he saw giant's walking through them; the Chaos Marines. He charged towards them, firing his last magazine for his bolter from the hip.

He fired five rounds into the first Night Lord, catching him in the chest and neck. The mass-reactive rounds tore his windpipe to shreds, and he fell to the floor, air entering his punctured lungs and collapsing them. He fired at the next one, sending three rounds into the traitor's head. The beheaded corpse followed his comrade to the ground_._ He fired seven rounds into the next one, three missing, but the other four proving easily enough that they would do the job. Three dead traitors, for three dead battle-brothers.

He fired two more shots before hearing a dull click, meaning the bolter had jammed. He threw the weapon away and held his chainsword in a two handed grip as he neared the Night Lords.

Cato's icon flashed red on his visor as he heard the familiar sound of bolter fire. Another name to avenge. He sidestepped the combat knife of the fourth Chaos Marine, before loping the arm off and swinging his chainsword down on his opponent's head, cleaving it in two. Natoris's icon flashed red as he unclipped the frag grenades strapped to his next enemy's belt, hearing the sound of a throat being slit and the gurgling that followed behind him. He pushed his attacker back, and the grenades quite literally left nothing left. It was only him standing now, against possibly seven Chaos Marines, fifty years of experience against possibly millennia.

He was tackled to the floor from behind, driving all of the wind out of him. Dozens of kicks and punches rained down on him. His armour cracked in several places. Eventually the beating stopped, and he was hefted to his feet. He thrashed, catching a Chaos marine in the jaw, sending the traitor sprawling.

This was rewarded with his helmet being ripped off and a vicious punch smacking his face. He saw stars as a body next to him was held up. It was Natoris. The Laraman cells in his blood had clotted the ragged slit in his throat, enabling him to breath. He also had his helmet taken off him. He nodded to the wounded marine, and received a nod in return.

The Chaos Marine that he had seen kill Marcellus and Castor stepped forward. He was clearly the leader of this warband, and held an ornate bolt pistol. The leader stepped right up to him, so much so that he could feel the ice-cold breath on his face. He promptly head butted the Chaos marine in the face.

He heard the nose crack, but was unable to see what happened as another flurry of punches rained down on him. The pain was almost blinding. The leader, with an obviously broken nose walked up to him again, but kept a distance this time.

"You have spirit for a young one." The leader said bluntly. "Shame, I'm sure you would have been an excellent lackey of the false Emperor."

"It's your gods that are false, heretic." He spat in return. The leader merely chuckled as a response.

"Maybe we're both right. Maybe we could have been brother's, in a better time, a better place, but no more." The warlord then calmly raised his bolt-pistol and shot Natoris in the head. He closed his eyes as he felt his friend and battle-brother's hot blood splash onto his face.

He heard the leader's breathing draw closer, and whisper in his ear. "But maybe I'm the one with the gun." He felt a flash of pain in the back of his head and then darkness.


	2. Chapter 2

Brother's End

A Warhammer 40,000 story

Chapter 1

The Sparring Halls, Macragge

He grunted with effort as he decapitated a combat servitor, sending the partially robotic head flying. . Spinning round, he sent a fist into the jaw of another, sending it into the wall ten metres away. Parrying a third's downward blow, he kicked a fourth servitor that was coming in behind him in the chest, crumpling its mechanical ribcage and sending it to the floor. He flicked away the third servitor's serrated blade, loping its hand off as he did so. He reversed the grip on his combat knife and thrust it into the servitor's forehead, severing the processor's connection to the body. _It's like dealing with an Ork warband_, he mused, _take out the head and the body will die._ The whole engagement lasted less than five seconds.

To his rear, he heard a single person clapping. A slow, steady applause. An old, Terran gesture and one he knew one Astartes in particular used. He turned around. The clapper was Scipio Vorolanus, a fellow Sergeant in the Ultramarines 2nd Company. The two of them were good friends, having been initiated at the same time. They had fought together ever since.

"Well met brother." Scipio greeted him, clasping hands.

"The same to you." He replied, a small smile on his face. Scipio was one of the few friends that were still alive, as his squad were an advance party, sent to secure a landing zone. And of course, getting onto the ground required a drop-pod, the least favourite part of the plan for him. The plan; not the execution.

"Is it true, about what you are doing?" Scipio asked him, confusion in his eyes. "I know you take the burden of your squad's death, but…"

"Yes Scipio, the rumours are true." He interrupted his friend. Scipio glared at him,

"But no one blames you for your squad's death. You followed the Codex to the letter. If the intel was right, it should have been overkill sending a whole squad."

"Aye, but next time I'm making sure it's all right before jumping in." He replied sarcastically. "And besides, what if our roles were reversed? What if it was you in my place, and I had been sent by Sicarius to try and dissuade you." Scipio looked stunned, and opened his mouth to answer. "No need, brother. It makes perfect sense, how he would send my closest friend to try and stop me from leaving. I do not blame you." He again interrupted Scipio, and again was glared at by said Astartes.

"Yes, he did send me, but not to dissuade you." He cocked an eyebrow at the statement. "He commands you to meet him in 2nd Company's main armoury. You will need your armour for this." Scipio finishes with a weak smile. They clasp hands one last time. "Good luck brother. You will need that too." They let go of each other, and walked their separate ways.

"As will you, to beat my score on the range." He shouted after his fellow Sergeant, who chuckled quietly to himself. They didn't say goodbye. They never did.

As he walked towards the armoury, he saw various Ultramarines training, praying, or maintaining their armour. Each one of them gave him a nod of respect. Word must have gotten around quickly about his request, and its acceptance. It struck him that this would probably be the last time he walked down Macragge's halls. He silently vowed that it wouldn't.

* * *

He reached the main armoury, hearing the whirring of servitors and smelling an overwhelming amount of oils. He walked slowly towards 2nd Company's section of the armoury. He found his captain, Cato Sicarius, tending to his sword. The blade was old, and originated from Sicarius's home on Talassar. Yet it was still as deadly in the right hands as it always was. "You asked for me, my lord." He said. Sicarius looked up from his power sword.

"Castus, yes, I did. I hope you are prepared?" He asked, setting his blade down on the table he had been working at and walked towards him.

"Yes, my lord, I just need to get back my armour from the Techmarines." He answered truthfully.

"Are you absolutely sure about this? No one will blame you if you choose not to." He asked Castus. It was a question the Chapter Master had asked him also. The Chapter had already lost nine battle-brothers in one action. A tenth would add insult to injury.

"Yes my lord. Those Chaos Marines deserve to die for what they did, and with the Great Devourer and Tau attacks becoming more frequent, I think the Chapter will need every brother it can get. Better to lose one on an impossible mission than have a strike-force unavailable if Ultramar is attacked." He gave the same answer that he had given the Chapter Master.

"Aye. You made a good sergeant, maybe even my successor in a few decades. Shame to lose you like this." Sicarius mused.

"I'm not dead yet Captain." He joked half-heartedly.

"True." He agreed. "I have something for you, to aid you on your quest. Follow me." Castus did as his captain said, and the two Astartes walked further down the armoury.

They reached a secluded chamber, which contained a chainsword, locked in a stasis-field. It had a golden light shining in the field, which highlighted the detailed golden eagle on the hilt. The blade itself was the same azure blue colour of an Ultramarine's power armour, and the serrated teeth were obsidian, a stark contrast to the hilt.

"The Sword of Theil. A mighty weapon, one that is now yours." Theil was an Ultramarine sergeant during the Horus Heresy. He had been marked for censure before the Heresy due to him running theoretical tactics on fighting other Space Marines. During the Battle for Calth, he used the tactics that he had been censured for to great effect, reaping a substantial casualty rate on the Word Bearers that attacked Calth. His tactics were adopted by the Ultramarine legion, and were written into the Codex Astartes. Castus turned to his captain.

"Are you sure my lord? If I fall…" He asked, unusually stunned by the gift.

"Then you'd better not fall." Sicarius answered, his haughty attitude back.

"Well, this is farewell. May the Emperor and the Primarch protect, captain." Castus made the sign of the Aquila with his giant hands.

"The same to you, sergeant." Sicarius replied, also making the sign of the Aquila. They then clasped hands. "Good luck, Castus, and bring me back that traitorous bastard's head."

* * *

**A/N: Hello, Bradykins98 here. I am really sorry about two things, firstly the amount of time it has taken to get chapter 2 on here, as I've had severe writers block with this story as well as other things. The second is the shortness of this chapter, as well as the fact it's a filler. I just needed something to get the ball rolling, and this is it. By the way, in case you didn't realise, the main characters name is Castus. **


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